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Help My poor ol 330A/BP

03-18-2019, 01:03 PM

Hi all. I am hear in hopes of finding info on my broken 330A/BP. It just happened. I used to work fine. I have not used in 2 years as I was building a new shop. I have not used the AC.
Here is what I have so far. When striking an arc, it has to be maxed out on the peddle/ dial and on HI setting. This results in just enough power to weld a 1/8in. Low setting won’t come close.
Current does go up and down with controls. Does not seem to work with HF on. But does in continuous. Work is grounded. Cleaned terminals. Can hear gas flow. HF dial was bypassed by previous owner.
SN HK243969. Down loaded manual. Check HF gap .009. Took panels off and blew out dust. Tried again and found resistor (core control set pt# 290) on top GLOWING bright orange! and varnish melting.
Diode appears to be OK. .5 volt drop one way open the other. I have ordered what I think will be proper replacement for these two parts but I doubt it will fix it.
I am contemplating purchasing another machine for parts. Anyone have any suggestions? I think I covered all I’ve done.

Try stick welding with AC, with the remote/std switch in the std position -- I'm hoping it will work, and the resistor shouldn't glow. The glowing resistor would account for low power output--and is glowing because you are getting a LOT of control current through the mag amp, which would increase core saturation and lower output. The problem is apparently somewhere in the mag amp control circuit.

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Thanks I will try that. I just have to make some leads. Haven't used it for arc yet. Used to have a Lincoln tombstone for that. Now I will show my ignorance ... what is the mag amp control circuit? same as core control set?

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Yes. Magnetic amplifiers use a magnetic core to control current. They are really an innovative design from WWII German buzz bombs. They are "sort of" a transformer. The amount of power transferred from the primary winding to the secondary of a transformer is determined by the strength and "motion" of the magnetic field in the iron core--there is no physical connection between primary and secondary. By varying the degree of magnetic saturation in the core (which is done by your weld amperage adjustments controlling a DC current in the control winding on the mag amp), you can control how much current is passed from the primary winding (power line) to the secondary (your weld output current). A relatively small change in control current can cause a big change in output current. A very cool device, pretty bulletproof, and so expensive to make that no one does it much any more, especially for welders. IGBTs and SCRs are cheaper and an incredible amount lighter. You have a rock-solid classic there; just need a forklift to move it around.

You're welcome. I find mag amps and transformers absolutely fascinating. So simple, there's really nothing to go wrong If well built--if you don't have everything nailed down very tightly they WILL burn up when vibration from the power wears the very thin insulation off of a winding and it touches the core--there's a LOT of smoke in these things to leak out. It's dramatic and really smells bad.

Started studying up on transformer and mag amp design characteristics lately--a really complicated field. Lots of fun math. I can see how a person could devote their whole life to it if they were really a geek and wanted to get really good. Miller obviously had/has some guys who really know how to do it, although probably not mag amps any more.

Another interesting sidelight--there was a huge battle (and a lot of bad blood at least on one side) way back when George Westinghouse and his employee Nikola Tesla (Westinghouse Electric) were engaged against Thomas Edison (General Electric) in deciding whether power distribution essentially the world over would be AC or DC. Edison said DC, with a power station about every block or so, while Tesla said AC, with a few huge power stations, high voltage transmission, and transformers everywhere. Obviously Westinghouse won the argument, (strictly based on the cost to implement it--pretty simple math) and Edison was pretty bitter about it, if what I have read is true. Edison even had public meetings in rented auditoriums as a last-ditch effort to win the argument. In the meetings, he electrocuted dogs to prove that while his DC would hurt the dog, it didn't kill it. The same voltage AC killed it, so it was obviously more dangerous and shouldn't be used. Nice guy!

There is a pretty non-technical book on that battle called Empires of Light. The author's writing and the editing leave a lot to be desired, but there is a great deal of very interesting information in it.

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Oh my word. Tesla was the man. I love the inventiveness. HiJack cool. Stick test interrupted. (late night lazy) Did get the stinger made. I'll get it to night. I assume 3 possibilities, weld good, welds poor, no weld. What COULD each scenario mean?